While Wonder Woman and Martian Manhunter are the central "Big 7" characters, this episode has much going for it. Again, the Legion Of Doom has set their sights on an artifact or person of historical merit. Grodd has something in store and finally gets called on it, but still isn't telling.
Death Ray (Really Black Mantra from Aquaman's rogue gallery) gets some shine and a nod to Lynda Carter's Wonder Woman are just some of the easter eggs this episode provides. The edits from the comic for the Viking Prince was a surprising touch for such a great animation team. It was also welcomed.
This episode is as much about J'onn as it is about the Viking Prince. J'onn, in JLU as well as in the comic version of JLA, has always been the mainstay. He finally takes a much needed leave of absence to get closer to earthlings and our strange habits. I can almost guarantee that he'll be back for the finale (Bats, Supes, Wondy or all three probably know how to get in touch with him) but with the Legion breathing down their throats, this is not the time to lose such a powerhouse and their telepathic leader. If you TiVoed this episode, better hold on to it, because I bet will become very important for the end run.
All in all - 9.5 out of 10